There are known conventional thread fastening tools used to facilitate an operation for tying a suture thread into a knot, which requires a particularly high degree of skill, in tissue suturing (for example, see PTL 1). The thread fastening tools are configured so as to be able to grip part of a suture thread through an operation that is easier than an operation of tying the suture thread. For example, a thread fastening tool disclosed in PTL 1 is formed of a cylindrical member having a hole into which a suture thread can be inserted, and the thread fastening tool is crimped with the suture thread inserted into the hole, thereby gripping an intermediate position of the suture thread.